(1) Field of the Invention
The present invention relates to an air defense system for a static structure such as a building in an urban environment.
(2) Description of the Prior Art
The tragic events of Sep. 11, 2001, when commercial aircraft were used to accomplish suicide attacks on office buildings, have emphasized the need to be able to provide some means of air defense to civilian structures in an urban environment. Such structures may again be targeted by terrorist agents using aircraft to deliver an explosive payload, in a suicide dive, or in a manner similar to that of a car bomb attack. Any aircraft, large or small, that approaches a building at very close range may be a threat. Therefore, there is need to develop concepts for defending urban structures from close encounters with airborne vehicles.
A traditional air defense system, such as is used by military forces, typically involves firing an explosive device (missile or projectile) at a threatening aircraft. It is conceivable that such a system could be mounted on an office building to provide an air defense capability. The obvious disadvantage of such a system is that its use would impose an additional lethal threat to the area, in that bullets or other elements of explosive ammunition would rain down upon nearby streets and could adversely impact civilian occupied structures other than the one that was being defended.
One type of missile defense system known in the prior art is shown in U.S. Pat. No. 5,400,688 to Eninger et al. This missile defense system generates a change in density in the air path of a missile. The density change is created by a high pressure water system which can be generated by a water jet or a body of water explosively created from a water surface. The change in density creates an effective barrier against an incoming missile.
It is also known in the prior art that water cannons may be used to neutralize a bomb. One such system for doing this is shown in U.S. Pat. No. 5,136,920 to Breed et al.
In an urban setting, a preferred defensive capability would be one in which something could be fired at close range against an incoming aircraft to deter its attack, but the spent ammunition would become harmless beyond a calculated short distance from the defended structure.
Further, a traditional air defense gun or missile launcher uses explosive chemicals to discharge or launch the weapon's payload. The presence of such material in an urban environment, such as an office building, is likely to be unacceptable. Therefore, a preferred defensive system would also be one that does not require explosive devices of any kind, either for launch or damage to the target.
As can be seen from the foregoing discussion, there is a need for an air defense system which avoids the difficulties associate with conventional air defense systems and which is viable for use in an urban environment.